This invention relates to a method of coating a hydrophilic polymer surface layer with an osmolality increasing compound to produce a more stable hydrophilic surface as well as medical articles being coated with said improved hydrophilic coatings.
Hydrophilic coatings have a much lower coefficient of friction when wet than when dry. Thus, the formation of hydrophilic coatings on substrates has many applications and, in particular, is desirable in many biomedical applications. For example, biomedical devices such as wound drains, catheters, surgical tools and other medical instruments intended for insertion in the body cavities are advantageously coated with a hydrophilic substance, because the instrument gives a good hand grip in dry condition while simultaneously becoming very slippery when it comes in contact with water-based liquids. Thus, the device can be inserted easily without causing trouble to the patient. Further, an article having a hydrophilic surface coating is desirable to minimize thrombosis, crystal formation, tissue trauma, tissue adhesion to medical instruments, and foreign body reactions. In prior art methods, surfaces have been rendered hydrophilic by such methods as high energy radiation in situ polymerization processes, by grafting, by forming an interpolymer network or by direct chemical bonding, for instance, by isocyanates or silanes. Such hydrophilic polymer surfaces for medical use are described for instance in G.B Pat. No. 1,600,963, U.S. Pat. No. 4,373,009, U.S. Pat. No. 4,459,317, WO 83/03977 and European Patent Application 83850090.8. Extensive studies indicate, however, that the hydrophilic coating can dry out, thus rendering the article insufficiently hydrophilic.